1. Field of the Invention
The present invention relates to a method for preparing a particulate release agent, and to a toner including the particulate release agent. In addition, the present invention relates to a method for preparing the toner.
2. Description of the Related Art
Electrophotographic image forming methods typically include the following processes:
(1) Forming an electrostatic latent image on an image bearing member such as a photoreceptor (latent image forming process);
(2) Developing the electrostatic latent image with a developer including a toner to form a toner image on the image bearing member (developing process);
(3) Transferring the toner image onto a recording material such as a paper sheet (transferring process); and
(4) Fixing the toner image on the recording material upon application of heat, pressure, a combination of heat and pressure, a vaporized solvent, or the like, resulting in formation of an output image (fixing process).
The developing methods are broadly classified into wet developing methods using a liquid developer including an insulating organic solvent and a pigment or dye dispersed therein, and dry developing methods (such as cascade developing methods, magnetic brush developing methods and powder cloud developing methods) using a dry toner including a binder resin and a colorant dispersed therein. Recently, dry developing methods are widely used.
The methods for preparing toner are broadly classified into dry methods typified by pulverization methods in which toner components such as binder resins and colorants are kneaded and the kneaded toner components are pulverized, followed by classification to prepare toner particles, and wet methods typified by polymerization methods in which toner particles are prepared using a suspension polymerization method or a polymer emulsion aggregation method. When pulverization methods are used, it is necessary to prepare toner particles having as small weight average particle diameter as possible to produce images having a good combination of resolution and half toner property. If fine toner particles having a particle diameter of not greater than 4 μm and coarse toner particles having a particle diameter of not less than 15 μm are removed in the classification operation to produce high quality images, the yield of toner deteriorates. In addition, pulverization methods have drawbacks in that it is hard to evenly disperse a colorant and a charge controlling agent in a thermoplastic resin, i.e., a colorant and a charge controlling agent are unevenly dispersed in a thermoplastic resin (binder resin), thereby deteriorating the properties of the toner such as fluidity, developing property, durability and image quality.
In attempting to remedy the drawbacks of the pulverization methods, polymerization methods such as suspension polymerization methods and polymer emulsion aggregation methods, in which a polymer emulsion, a colorant and a charge controlling agent are mixed and the mixture is heated to aggregate the polymer, resulting in formation of toner particles, have been proposed.
In addition, there are proposals for a granulation method in which a toner including a polyester resin is granulated in water using an organic solvent, and a polymerization method in which a prepolymer having an isocyanate group is reacted with an amine compound to prepare toner particles.
Heat fixing methods using a heated fixing member such as rollers have been mainly used for the fixing process. In order to prevent adhesion of toner images to such a heated fixing member, a technique in that an oil is applied to a fixing member has been used. Recently, a technique in that a release agent is included in toner has been mainly used to prevent adhesion of toner images to a heated fixing member. However, such a toner often causes a toner adhesion problem in that the toner adheres to an image bearing member.
For these reasons, the present inventors recognized that there is a need for a toner which can be produced at a high yield although the toner has a small average particle diameter and includes a release agent and which can produce high quality images over a long period of time without causing the toner adhesion problem.